The Great Lakes have been invaded more than any other freshwater system in the world, with nearly 190 non-native species having established populations in the basin over the past two centuries. A recent study suggests that a binational regulation targeting ship ballast water has had a remarkable suppressive effect on the invasion rate.
Anthony Ricciardi, lead author of the study, is a professor at McGill University. He studies invasive species, especially aquatic invasives. “I’ve been following the invasion history of the Great Lakes for a few decades now,” he told The Expositor.
“My students and I have been involved in examining the impacts of things that arrive, including those that arrive in ballast tanks,” he said. “In this particular case, I’ve been following the invasion rate for awhile.”
The study compared 13 years before 1993 where there was no regulation, 13 years intervening between 1993 and 2007 with partial regulation, and then 13 years with full regulation after 2007. There was a big drop in the number of species found established after the full regulation went into effect.
“This layer of protection is clearly beneficial. There are many highly invasive freshwater species in Europe, for example, that could be delivered in ballast water and would almost certainly proliferate in the Great Lakes. The regulation is likely preventing their introduction.”
The majority of non-native species have been introduced to the Great Lakes through ballast water release by ships crossing the ocean. Ballast water release was responsible for introducing several of the most disruptive things in the basin, including zebra mussels, quagga mussels and the round goby.
In a bigger context, Professor Ricciardi explained, ballast water release from ocean vessels has introduced hundreds, perhaps thousands, of invasive species to coastal ecosystems worldwide. “Some of these species have caused documented impacts on biodiversity, on ecosystem functioning, and some have had impacts on human well-being by affecting fisheries and human health.”
The opening of the St. Lawrence Seaway in 1959 allowed larger vessels, which carried more ballast water, and more frequent ship traffic into the basin. Since its opening, 65 percent of invaders in the Great Lakes have been linked to ballast water release. The remaining invaders have been introduced through other vectors, including aquarium dumping, bait bucket dumping, canals, aquaculture escapes and intentional releases. “I’m not diminishing the roles of these other vectors,” he said. “I’m saying the principle one has been ballast water.”
From 1959 to 2006, one new invader was discovered established in the Great Lakes every six to seven months on average. They include some of the most disruptive species ever seen in the basin, including zebra mussels, quaqqa mussels, the round goby and the spiny water flea.
Ballast water was first recognized as a problem in the 1980s, even before the zebra mussel was introduced and eventually, both Canada and the United States decided to implement regulations to deal with it. The first regulation, introduced by Canada in 1989, was voluntary. Four years later, in 1993, harmonized ballast water regulations were introduced.
The 1993 attempt failed. The regulation required ships destined for Great Lakes ports to exchange their ballast water on the open ocean prior to entering the Seaway. The idea was that any freshwater organisms in the tanks would either be purged during this exchange or killed on contact with the high-salinity sea water as it comes in, breaking the connection between freshwater organisms being carried overseas by ships and released in the Great Lakes.
In spite of the regulations, ballast water mediated invasions occurred in subsequent years, because there were loopholes.
Some ships were able to declare their ballast water to be unpumpable and didn’t have to undergo the procedure, and were not covered by the regulation. These comprised the majority of the vessels entering the basin and their ballast tanks still contained sediment. These ships would take on and release water as they moved from port to port on the Great Lakes.
Organisms living in that sediment would get resuspended and then released into the lake system. “That’s why those ships were an invasion risk,” stated Professor Ricciardi. “They weren’t covered. That was the loophole.”
Professor Ricciardi’s data, published in 2006, showed that the invasion rate remained steady, even after 1993. “This added some impetus for creating new regulations,” he said.
Scientists had been testing new ways to treat ballast water. Saltwater flushing, where water is pumped out of the tanks at the same time as sea water is pumped in, was found to be the most practical method. Eventually there will only be salt water in the tanks, and experiments showed this procedure to be quite effective in reducing the number of living organisms there, he noted.
By 2008, both Canada and the US had mandated saltwater flushing of ballast tanks before ships entered the Great Lakes. This regulation was enforced through inspection.
“The true test of such a regulation was its effect on the observed rate of species invasion because that’s what it’s meant to control,” he said. “Since 2008, after 13 years of data, invasions in the Great Lakes basin declined by 85 percent. They have never declined by that. They may have fluctuated in the past but they have never had such a steep decline. Now they’re at their lowest invasion rate in two centuries. We have never received so few invaders over such a period of time in any other time in the history of the Great Lakes basin. “
Other factors could have, to some extent, contributed to this abrupt decline, such as increased public education to stop people from dumping things from their aquariums, and regulations to ban certain species known to be problematic, but “the empirical evidence points to ballast water regulation as the overwhelming primary cause of this suppressed invasion rate.”
He pointed out that while regulations have substantially reduced the risk of ballast water invasions, it is still possible that ballast water could contribute to invasions by organisms that have broad tolerance to salinity, or that can reproduce in very small numbers. “That requires further research. But I am pretty confident in saying that the ballast water regulation was very likely responsible for this unprecedented drop in invasion rate.”
The Great Lakes basin remains at risk of invasion from other vectors, especially those associated with live trade, that is fish associated with living species such as fish and plants sold through the aquarium trade, fish and plants sold through the ornamental garden trade, fish sold as bait, fish sold through food markets and so on, added Professor Ricciardi. “But I can’t think of another case where the invasion rate of an aquatic system has been so extensively suppressed through management intervention.”
“Species have always changed their distributions but under human influence, species are moving faster, farther and in greater numbers than in any other time in earth’s history,” he warned. “Modern invasions are another form of anthropogenic change, except they interact with every other form of global change including climate change, which is going to drive species from the south to move north, including in the Great Lakes. If they can get in, there’s going to be sunfishes and basses that are warm water species that are moving north. It will all depend on whether the canals will allow them to get in.”
Species that normally couldn’t establish in the Great Lakes might be able to in 10 years time, and species that are doing very well now might not do so very well in the future: the system is changing, he said.
“I’m pretty confident in saying that this intervention, if it continues as we’ve being seeing, will have kept out many disruptions that would have cost us in some way,” said Professor Ricciardi. “Remember that there’s a fishery in the Great Lakes basin that’s worth several billion dollars to both countries. Let’s not underestimate the socio-economic importance of reducing the risk of invasion by controlling the dominant vector as effectively as this regulation appears to be doing. This needs to be highlighted as an example of what can happen when multiple stakeholders work together on an evidence-based solution.”
By that he means one that is recommended by science, put into policy, and enforced through inspection.
“The Great Lakes are a shared transboundary resource, affected by transboundary problems, because invasive species don’t respect borders,” he continued. “This is an example where binational regulation was required and in this case, seems to have worked.”
“Let me make this clear, and this is important,” Professor Ricciardi added. “The Great Lakes are still vulnerable to invasive species, especially from other vectors. I don’t want people to think that the problem of invasion of the Great Lakes is solved. It isn’t. It has been mitigated greatly because of the (ballast water) intervention.” Interventions are still necessary for other vectors.
Lori Thompson, Local Journalism Initiative Reporter, The Manitoulin Expositor